23 research outputs found
Behaviour of a double layer tensegrity grid under static loading: identification of self-stress level
International audienceThe determination of the state of internal stress is important to define the rigidity of a tensegrity structure and its stability. Severalmethods can be used; some are based on direct measurements of the forces in the elements, but are not easily transferable to a real structure.The authors opt for indirect measurement techniques, which seem more appropriate for implementation on-site. One can consider thevibratory anal-ysis of the elements, the vibratory analysis of the whole structure, or the analysis of the structureâs behavior under staticloading. Here, the node displacement fields of a tensegrity structure in different states of self-stress under several strategies of static loadingsis studied by comparing the measurement obtained by a tachometer with simulations. The aim of this work is to show the feasibility of adisplacement field to identify the state of self-stress by this analysis. It is shown that under certain conditions, plans can be made to replacethe direct measurement of the forces by indirect analysis
Indigenous community grounded research. Perspectives from Atikamekw Youth (Manawan, Nitaskinan, LanaudiÚre, Québec, Canada).
In this session, we will discuss the history, the structure and the impacts of the Matakan project, a participative research project designed for promoting and passing down atikamekw knowledge to young people of the Atikamekw community of Manawan (LanaudiÚre, Québec). We will address issues related to the decolonization of research and knowledge, and show how this project is also part of the Atikamekw strategies and priorities related to education and youth
Le modelĂ© dâĂ©rosion glaciaire de lâĂźle dâAnticosti rĂ©vĂ©lĂ© par lâimagerie LiDAR
Des images LiDAR Ă haute rĂ©solution dĂ©voilent des modelĂ©s dâĂ©rosion glaciaire inĂ©dits qui nuancent fortement les interprĂ©tations publiĂ©es antĂ©rieurement concernant lâhistoire glaciaire de lâĂźle dâAnticosti. SculptĂ©es dans le roc, ces formes dâĂ©rosion glaciaire sont trĂšs diversifiĂ©es : lacs de surcreusement glaciaire, drumlins rocheux, cannelures gĂ©antes, mĂ©gaqueues-de-rat, dalles de roc dĂ©placĂ©es par les glaciers. Bien que pour la plupart discrĂštes, ces formes dâĂ©rosion glaciaire sont prĂ©sentes partout sur lâĂźle. Toutefois, câest dans les basses terres de lâest et de lâouest que lâempreinte glaciaire est la plus forte. Dans les basses terres de lâest, lâĂ©coulement glaciaire vers le sud-ouest, observĂ© partout sur lâĂźle, a Ă©tĂ© suivi par un Ă©coulement vers le sud-est. Ces 2 écoulements avaient leur source sur le Bouclier canadien (inlandsis laurentidien). Un Ă©coulement tardif vers le nord a Ă©tĂ© observĂ© dans la moitiĂ© nord du plateau central (au nord de la riviĂšre Jupiter). Cet Ă©coulement vers le nord est attribuĂ© Ă la calotte glaciaire rĂ©gionale qui a occupĂ© le plateau central durant la dĂ©glaciation.Recent high-resolution LiDAR (Light Detection and Ranging) images of Anticosti Island (QuĂ©bec, Canada) have revealed novel landforms created by glacial erosion that strongly nuance the previously published understanding of its glacial history. These diverse forms of glacial erosion include feature carved into the bedrock, such as glacially overdeepened lakes, rock drumlins, giant grooves, and mega crag-and-tails, as well as slabs of rock displaced by glaciers. Although mostly relatively inconspicuous, these forms of glacial erosion are present throughout the island. However, the glacial imprint is strongest in the eastern and western lowlands. In the eastern lowlands, the southwestward ice flow that occurred everywhere on the island was followed by a southeastward flow. Both these flows originated on the Canadian Shield (Laurentide Ice Sheet). Indicators of a late northward flow were observed in the northern half of the central plateau (north of the Jupiter River). This northward flow is attributed to the regional ice cap that occupied the central plateau during deglaciation
Mechanical behaviour in compression of a foldable tensegrity ring: parametric study and rheological model
International audienceTensegrity rings, sometimes also called hollow ropes, tubes or sleeve modules, are systems based on straight prism geometry and composed of one or more bar circuits and cables. Recently, we developed a general study for these structures, including their ability of folding. We designed and built a human-size prototype of a pentagonal tensegrity ring with 30 cables and 15 bars, connected to 15 nodes symmetrically spread on three layers. This prototype has been tested under compression loading in several experiments. Finite element (FE) simulations are consistent with the experimental observations. In this paper, we present an analytical model of the axial behaviour of such a ring. We show the influence of each element on the mechanical behaviour of the structure, and our study can be seen as a first step in adapting the response of the system to a static or dynamic behaviour. We also provide a rheological model for its axial behaviour under compression. Our model is reduced to four springs and gives an axial mechanical behaviour identical to that obtained by FE simulations. Thus, a macro-element tensegrity ring is presented which connects the axial symmetrical load to four nodal displacements
Modélisation analytique du comportement en compression d'un anneau de tenségrité à base pentagonale
Ce document propose une étude analytique du comportement d'un anneau de tenségrité à base pentagonale. Il permet d'évaluer l'influence de chacun des éléments sur la rigidité globale du systÚme. C'est une premiÚre étape en vue de l'adaptation et le contrÎle de ces systÚmes, en fonction des actions qui lui sont appliquées
Le rĂŽle de la morphologie dâune succession seuil-mouille dans la croissance quotidienne et lâĂ©volution dâun couvert de glace
MenĂ©e sur un tronçon de riviĂšre de taille moyenne, cette recherche analyse quotidiennement les processus de formation et de croissance de la glace dans une riviĂšre graveleuse caractĂ©risĂ©e par une succession seuil-mouille. Elle documente Ă©galement lâeffet de la morphologie du chenal et des conditions hydromĂ©tĂ©orologiques sur la croissance et lâĂ©volution du couvert de glace. Des photographies numĂ©riques perpendiculaires au chenal et une documentation des caractĂ©ristiques morphologiques du chenal et de la glace ont Ă©tĂ© rĂ©alisĂ©es quotidiennement. Les rĂ©sultats montrent que la glace apparait simultanĂ©ment dans les seuils et la mouille, mais que la formation complĂšte du couvert de glace survient un mois plus tĂŽt dans la mouille. Cette diffĂ©rence sâexplique par des mĂ©canismes de croissance variables selon les unitĂ©s morphologiques. Dans les seuils, la glace croit des berges vers le centre du chenal par accumulation de particules de frasil et par la croissance de la glace thermique. La croissance du couvert se produit Ă©galement autour des blocs protubĂ©rants dans le centre du chenal grĂące Ă lâĂ©mergence de la glace de fond. Dans la mouille, le couvert de glace progresse Ă partir des berges vers le centre du chenal principalement par la glace thermique, mais aussi par accumulation de minces particules de frasil. Dans les seuils et la mouille, les taux de croissance quotidiens cumulĂ©s rĂ©vĂšlent des profils similaires avec une transition marquĂ©e dans la vitesse de croissance du couvert (rapide/lente). Le suivi quotidien de la couverture glacielle a permis de documenter la dynamique de formation et lâĂ©volution spatio-temporelle de la couverture glacielle. Une coulĂ©e de neige liquĂ©fiĂ©e est survenue au mois de janvier dans un tributaire mineur et a provoquĂ© la dĂ©sorganisation de la morphologie glacielle ainsi que la formation dâun imposant cĂŽne glaciel Ă la confluence.This study analyses the daily processes leading to the creation and evolution of the ice cover in a riffle-pool sequence of a medium-sized river. The study also documents the effects of channel morphology and of hydrometeorological conditions on ice cover creation and evolution. Digital photographs taken perpendicularly to the channel were used to characterize ice and channel morphology. Results show that although ice cover formation is simultaneous, complete ice coverage of the pool occurs a month earlier. This significant time difference can be explained by distinct ice growth mechanisms for each morphological unit. In riffles, the ice growth occurs from the banks to the center of the channel, attributable to frazil particle accumulation and thermal ice growth. In riffles, anchor ice on the river bed contributes to the ice cover growth, as well as thermal growth around some protruding boulders in the middle of the channel. In pools, the ice cover progresses from the banks to the middle of the channel mainly by thermal ice growth, and also by fine frazil particle accumulation. Cumulated daily ice growth rates are similar in both pools and riffles, with both showing a clear transition in ice growth speed from quick to slow. The spatio-temporal ice growth and evolution dynamics were documented by the daily reviewing of the ice cover. In January, a slushflow from a minor tributary disorganized ice morphology and created an imposing ice cone at the confluence
Mesure de la tension de cùbles à rigidité de flexion non nulle à l'aide d'un tensiomÚtre
10 pagesNational audienceLe contrĂŽle et le rĂ©glage des structures de tensĂ©gritĂ© nĂ©cessitent la mesure de la tension des cĂąbles en place. Un modĂšle empirique de flexion trois points, prenant en compte l'inertie de flexion du cĂąble, est dĂ©veloppĂ© pour un tensiomĂštre d'espacement 20 cm entre poulies. La courbe expĂ©rimentale (F, d) du tensiomĂštre obtenue pour le cĂąble installĂ© sur banc de tension permet, aprĂšs rĂ©gression polynomiale, l'Ă©valuation de l'inertie de flexion du cĂąble. Un essai au tensiomĂštre sur le cĂąble installĂ© dans la structure permet ensuite d'obtenir avec une excellente prĂ©cision la tension en place. Avec une incertitude plus importante, la raideur des appuis peut aussi ĂȘtre Ă©valuĂ©e
Structural design and active control of modular tensegrity systems
International audienceTensegrity systems are self stressed reticulate structures composed of a set of compressed struts assembled inside a continuum of tendons. This principle is at the origin of lightweight and transparent structures that can cover large spaces and be erected, in particular cases, by deployment. In this paper, we propose a general design and optimization procedure adapted to modular structures following this principle. An application is presented on the case of a curved deployable footbridge.Besides, as lightweight frames, these systems are subject to deformation and vibration issues when faced to varying actions such as climatic, human, orseismic loads. Active control is as solution that allows, using actuators integrated into the structure, to attenuate these effects. On the case of a real plane modular tensegrity grid, we present a specific methodology for the active damping of the first two modes and its experimental validation